Science —

Chain reaction: the (slow) revival of US nuclear power

For the first time in over 30 years, a new nuclear plant has been approved—but …

The next generation of nuclear reactors

According to the report, the nuclear energy portfolio in the near future is likely to be made up of advanced versions of the current light water fission reactors (Generation III), along with Generation IV and small, modular reactors.

Generation III reactors were designed as improvements to those currently operating in the US, emphasizing simplification, standardization, and passive safety features. However, after the Three Mile Island and Chernobyl accidents, no Generation III plants were ever constructed. More recently, updated versions of these designs (known as Generation III+) were developed, and are in the process of being licensed. The recently approved Westinghouse AP-1000 is one such example.

The next generation of commercial reactors, Generation IV, are all still in the research and design phase, but promise significantly higher performance, safety features, and sustainability.

The next generation of commercial reactors, Generation IV, are all still in the research and design phase, but promise significantly higher performance, safety features, and sustainability. The development of Generation IV reactors began in the US in 2000, but since then 12 additional countries joined in the research program.

There are six specific reactor concepts that fall in this category: Very High-Temperature Reactor (VHTR), Super-Critical Water-cooled Reactor (SCWR), Molten Salt Reactor (MSR), Sodium-cooled Fast Reactor (SFR), Lead-cooled Fast Reactor (LFR), and Gas-cooled Fast Reactor (GFR). The first three are thermal reactors that operate at high temperatures, providing heat for non-electricity purposes. The second three are fast reactors that could function as breeders or nuclear waste burners.

Out of these six, two in particular have been studied and developed further: the VHTR and SFR.

The VHTR is designed to operate at temperatures as high as 1000°C in order to provide the heat needed for industrial processes such as steam reforming of natural gas, coal gasification, and hydrogen production via the sulfur-iodine cycle. This would allow the reactor to serve as a source of both electricity and alternative liquid fuels. However, conventional light water reactors are limited by the boiling point of water, so instead coolants such as gases, supercritical water, or molten salt must be used to reach such high temperatures. In addition, new construction materials would be needed to withstand high-temperature operation.

The US actually built two prototype VHTRs using helium as the coolant: Peach Bottom 1, which operated from 1966 to 1974, and Fort St. Vrain, which operated from 1977 to 1992. Helium is used in most VHTR designs since it is inert, remains in the gas phase, and doesn’t become radioactive (unlike most other coolants). Research on helium-cooled VHTRs is ongoing, funded by the DOE Office of Nuclear Energy. The main challenges are sustained operation at such high temperatures.

SFRs, on the other hand, are fast neutron reactors that use liquid sodium coolant. The world’s first nuclear power plant capable of generating electricity, the Experimental Breeder Reactor I (1951-1964, in Idaho) was actually an SFR. The US built and operated two additional experimental SFRs: the Experimental Breeder Reactors II, operated from 1964 to 1994, and the Fast Flux Test Facility, which ran from 1982 to 1992. The main challenge in developing SFRs is the explosive interaction between sodium and water—steam being the working fluid used to actually generate electricity.

Like all other fast reactors, SFRs haven’t yet been demonstrated commercially. No fast reactors are currently generating electricity in the US.

Small modular reactors

Multiple companies are developing small modular reactor designs, including the Westinghouse IRIS (left) and Babcock and Wilcox mPower (right).

The authors also predict greater use of small modular reactors (SMRs). These would generate between ten and 300 MW, compared with 1 GW from a larger plant. The main benefit here is the significantly lower upfront cost. Utilities could purchase one or multiple SMRs sized to provide the capacity needed, and then incrementally add modules later if the electricity demand increases. Each module would be completely self contained, and some designs can operate for years before refueling is needed.

Large nuclear reactors are typically built custom, so nuclear power never really achieved an economy of scale. SMRs, on the other hand, could be standardized and mass produced.

The NRC hasn’t yet approved any SMR designs, but multiple companies and research groups have been developing them since the 1970s. Designs using water, helium, sodium, lead, and fluoride salt coolants are all being considered, although the first commercial reactors will likely use the familiar light water reactor technology.

To give you an idea of the size, Westinghouse designed an SMR based on their larger AP1000 reactor. Compared with the AP1000’s 1100 MW electrical power output, the SMR would generate around 225 MW. All of the reactor components fit inside a containment vessel a little under 30 meters high and 10 meters in diameter. Like the AP1000, in includes passive safety systems. This design could remain cooled for seven days without any human intervention.

Many other companies are also designing SMRs. Babcock & Wilcox is working on a 160 MW, pressurized light water reactor design called mPower that might cost $600 million.

NuScale Power is developing an even smaller pressurized light-water SMR (creatively named NuScale) that would sit in in an underground water-filled pool. Each NuScale reactor module, at 45 by 9 meters, would generate 45 MW; a combined reactor building with 12 SMRs would generate a total of 540 MW. Unlike other designs that use pumps to circulate water, the NuScale reactor relies on natural convection.

The NuScale SMR relies on natural convection to circulate coolant water, and would sit underground.

Toshiba, on the other hand, is heading in a different direction by developing a small fast reactor that uses a liquid sodium coolant: the Toshiba 4S (Super Safe, Small and Simple) reactor. The 4S actually has the smallest electrical power output of the SRMs listed here at 10 MW. As with some of the others, it would sit underground, and could run for 30 years before needing to be refueled. This actually might be the first deployed SMR: Toshiba is working with the remote city of Galena, Alaska, to use the 4S as the first non-military nuclear plant in the state.

Another company, Hyperion Power Generation, is developing a 25 MW fast SMR that uses a lead-bismuth eutectic liquid-metal coolant (this falls in the Generation IV LFR class). Unlike most other reactors that use uranium dioxide as fuel, the Hyperion Power Module would use uranium nitride. This has a higher melting point and thermal conductivity than the typical fuel, which is beneficial at the higher operating temperatures of liquid-metal cooled fast reactors. With this SMR, instead of refueling every couple years, the entire 20-ton module is designed to be replaced every 7-10 years.

About the report

The Federation of American Scientists (FAS) tasks itself with “providing rigorous, objective, evidence-based analysis and practical policy recommendations on national and international security issues connected to applied science and technology.” Originally founded in 1945 by Manhattan Project scientists with the goal of preventing nuclear war, FAS has since expanded its focus to issues like biosecurity, energy security, arms sales monitoring, government secrecy, and terrorism.

The new report was composed and edited by Charles D. Ferguson, nuclear policy expert and President of FAS, along with Frank Settle, chemistry professor at Washington & Lee University.

The authors of various sections include a veritable pantheon of nuclear energy and policy experts: John F. Ahearne, former executive director of Sigma Xi and former commissioner (1978-1983) and chairman (1979-1981) of the NRC; Albert V. Carr, Jr., professor at Washington & Lee University focusing on energy law; Harold A. Feiveson, scientist at Princeton University studying nuclear weapons and nuclear energy policy; Daniel Ingersoll, Senior Program Manager for Nuclear Technology Programs at Oak Ridge National Laboratory; Andrew C. Klein, a professor of nuclear engineering at Oregon State University; and Richard Wolfson, professor of physics at Middlebury College, among others.

The report is quite detailed (and long—144 pages), and provides a good history of nuclear power in the US to explain how we arrived in the current situation.

Prospects for the future

The report is actually a bit contradictory on the future of nuclear energy. On the one hand, the authors of the report believe there is something of a “nuclear revival” underway, based on the large number of new applications for construction permits. In fact, some construction has even begun at Plant Vogtle in Georgia, where the NRC just voted on February 9 to allow the construction and operation of two new plants. A total of 20 applications have been filed to construct and operate 28 reactors at 18 different sites around the country. In addition, there are a couple of new reactor designs currently under review by the NRC.

On the other hand, the authors project slow progress at best. As I mentioned above, the high cost of new nuclear plants is a major barrier. Without some sort of carbon pricing to incentivize clean energy, the low cost of natural gas threatens interest in additional nuclear power plants. In addition, the federal loan guarantees currently favored to fund new plants are not sufficient, and likely not in the best interests of the public.

Low-cost SMRs may offer a solution to the cost problem, and help revitalize the industry. However, none have yet been approved by the NRC.

According to David Biello at Scientific American, only the two plants in Georgia plus another three elsewhere are likely to be constructed in at least the next decade. If there is a nuclear revival, it’s likely to be a slow one.

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Kyle Niemeyer
Kyle is a science writer for Ars Technica. He is a postdoctoral scholar at Oregon State University and has a Ph.D. in mechanical engineering from Case Western Reserve University. Kyle's research focuses on combustion modeling. Emailkyleniemeyer.ars@gmail.com//Twitter@kyle_niemeyer